The Volume Oscillator calculates the difference between two moving averages of the volume. The difference can be calculated as either the point ($) or percent (%) difference. When the indicator crosses the zero line, it signifies that the moving averages have crossed. When the indicator rises above zero, the first moving average has risen above the second moving average; when the indicator falls below zero, the first moving average has fallen below the second moving average.

Therefore, when the indicator rises above zero, the volume trend is increasing; similarly, when the indicator falls below zero, volume is decreasing.